The invention relates to a transformer comprising a transformer tank generally shaped like a rectangular prism and filled with insulating liquid and assembled mainly by welding and comprising four substantially vertical walls and two substantially horizontal walls, one of which is a detachably fastened transformer cover plate, and a transformer core placed in the transformer tank while the cover plate is detached.
Although the transformer of the invention can be applied in all normal operational environments, it is particularly suitable for use in confined surroundings, such as ships. The transformer is suitable for use for example as what is known as a transformer for internal consumption with which the voltage generated by a ship""s generators is lowered to the level of 230/400 V.
The use of a conventional oil-insulated transformer onboard a ship is restricted by the fact that the transformer core has to be lifted out of the tank during malfunction, whereby it requires vertical space that is about twice the height of the transformer. Furthermore, the xe2x80x98intermediate floorxe2x80x99 above the transformer has to be made solid enough so that the core supported by the floor can be lifted out of the tank with a pulley.
Onboard ships, air-insulated dry transformers are quite generally used, whereby free space above the transformer is not necessarily required, since the transformer is not placed in a closed tank, but is only protected by a casing which can be removed on site from around the transformer core during malfunction. Furthermore, such type of a transformer is by definition fireproof. However, the structure of an air-insulated dry transformer is more expensive than a conventional transformer using oil or some other insulating liquid as insulation. A frequently used solution is a conventional tank structure of a supply transformer with an upper space designed so as to allow freeing the lifting space in order to repair the transformer.
It is an object of the present invention to provide a transformer whose tank, containing oil or another insulating liquid, can be opened to allow a fault in the transformer core to be repaired without the transformer core having to be lifted out of the tank, whereby no free space above the transformer is needed. This object is achieved with the transformer of the invention, which is characterized in that at least one of the substantially vertical walls of the transformer tank comprises a detachable wall portion whose detachment allows the transformer core to be removed from the transformer tank through an opening formed during the detachment of the wall portion. Consequently, the transformer of the invention can be repaired by opening the side of the transformer tank and by pulling the core out without any need for more vertical space during repairs than during normal operation of the transformer.
In accordance with the above, an essential feature of the transformer of the invention is that, except for the tank, it is composed of standard components and can be assembled mainly by the same working methods that are applied in the assembly of standard transformers (lifting the core into the tank, oil filling). Since a transformer very rarely breaks down, it is economically significantly more advantageous to modify a conventional transformer in the manner described in the invention to a transformer which fits into low spaces, such as ships, than to design a completely different transformer structure for use in ships.
In a preferred embodiment, the detachable wall comprises an edging that projects outwardly from the level of the wall portion, i.e. outwards from the inside of the transformer tank, the transformer tank wall surrounding the detachable wall portion comprises an edging corresponding to the edging of the detachable wall, and the edging of the detachable wall portion and the edging of the transformer tank wall surrounding the detachable wall portion are welded liquid-tightly together at their outer edges, allowing the detachment of the wall portion by cutting off the outer edge of the edgings. Accordingly, in the transformer of the invention, the tank is assembled by welding, and the detachable wall portion is also fastened by welding to the rest of the tank casing, i.e. in practice the bottom plate, to the residual part of one of the short sides and the plates of the long sides. Since the transformer very unlikely breaks down, the detachable wall portion can also be fastened by welding and, when needed, opened by an angle cutter. When the detachable wall portion is fastened in the aforementioned manner, the entire seam fastening the detachable wall portion can be cut off when the wall portion is detached, and the seam can be made in a new place when the tank is reassembled.
To prevent debris originating from the detachment or fastening of the wall portion from entering inside the transformer, the transformer tank wall surrounding the detachable wall portion comprises sealing lining arranged inside the transformer tank, against which the surface of the detachable wall portion that is on the inside of the transformer tank is sealed.
In order for easy and simple removal of the transformer core from the transformer tank, it is preferable that the transformer core is adapted to rest on a glide plate, allowing the transformer core to be pulled out from the transformer tank resting on the glide plate.
Furthermore, it is preferable that one or more fasteners to allow the transformer core to be pulled out from the transformer tank together with the detachable wall portion are arranged between the transformer core and the detachable wall portion.